It's one thing to believe that there are other forms of life in the universe, but another to claim to have actually seen them.

Just think about it: the universe has trillions of galaxies, which have trillions of stars, and those stars have many of their own planets. It's a lot to take in, but there's an undeniable possibility that life exists outside of planet Earth.  

However, alleged UFO sightings, mermaids, and seeing green alien life forms are tales that should be strictly for science fiction movies.

1. Russell Crowe

The Oscar-winning actor shared a video in early 2013 supposedly capturing a UFO sighting.

The pictures were taken outside his office in Sydney, Australia. He tweeted, "A friend and I set up camera to capture fruit bats rising from Botanic Gardens. This was a big surprise."

If that doesn't look photoshopped, I don't know what does...

2. Khloe Kardashian & Kendall Jenner

After seeing some "spooky" lights in the sky, these "it girls" took to Twitter convinced that they experienced their first UFO sighting.

These tweets below are pretty self-explanatory.

"Khloe and I are freaking out right now over this UFO situation," wrote Kendall.

"I believe!!!! "@KendallJenner: you guys..I swear I just saw a UFO," tweeted Khloe.

Turns out the lights were a planned Trident II (D5) missile test flight, but these half-sisters beg to differ.  

Khloe had a response for the US Navy: "What do we expect people to say? Obvi they are going to say it's a meteor shower. I'm such a conspiracy theorist let me enjoy this."

3. Billy Ray Cyrus

The "Achy Breaky Heart" singer not only thinks the mullet should make a rebound, but that alien life has visited Earth.

In 2011, he tweeted about his first alien encounter: "O.K... my first UFO sighting. Looks like 5 or 6 disk like shapes hovering. Special moment 4 DAD."

In 2014, Miley was in the Bahamas when she questioned the object that "zipped" in the sky.

"My dad told me it was a satellite. But the way it zipped off was really weird."

4. Sigourney Weaver

Who better to believe in aliens than Alien star Sigourney Weaver?

In a 2011 interview with German magazine TV Spielfilm, Sigourney said, "I think there's a department in [the US] government which is exclusively dedicated to quashing reports about aliens. And that's so unfair. It would be nice if we weren't just able to read about it in the tabloids."

One of these next celebrities thinks she actually came in contact with an alien life form...

5. Fran Drescher

The Nanny actress's favorite story is the time she and her ex-husband, Peter Marc Jacobson, were abducted by aliens.

"You know, it's funny because Peter and I both saw [aliens] before we knew each other, doing the same thing, driving on the road with our dads," Fran told the Huffington Post back in 2012. "We were both in junior high. A few years later, we met, and we realized that we had the same experience. I think that somehow we were programmed to meet. We both have this scar. It's the exact same scar on the exact same spot."

Fran is convinced that aliens programmed a chip inside her, and that's the reason she has a scar.

After the story was published, she published this tweet: "I'm a Comedian& if u don't believe me ask my alien ;) lol."

Some believe she was trying to save face.

6. Nick Jonas

The former Jonas Brother still thinks about the alleged UFO he saw when he was a teenager.

"I was in my backyard in L.A., and I looked up at the sky and [saw] three flying saucers," Jonas said in 2015. "I looked at my friend and said, "˜Are you seeing this or am I losing my mind?'."

His friend apparently confirmed "he was seeing the same thing. Then I went online and looked and there were three identical sightings, two weeks before."

7. Jaden Smith

Will Smith's 19-year-son says that he had a conversation with former President Barack Obama who confirmed his belief about aliens.

"I talked to President Obama about extraterrestrials. He said he could neither confirm nor deny the existence of aliens, which means they're real. If people think we're the only people that live in this universe, then something is wrong with them."

Aliens are also his favorite topic of conversation.

"I like aliens!" he told Wonderland. "I think aliens are really cool, because they exist."

8. Kesha

Pop singer Kesha is trying to convince the world that she's seen alien spaceships.

She posted a photo of herself wearing a shirt with a UFO on it with the caption: "ufos are real. i have seen them. not playing."

"I was in Joshua Tree, totally sober, let me preface"”completely fucking sober... I think people would be like, 'She was on acid' or something. I wasn't. I was on nothing. I was a totally sober Sally, just a lady in the desert," she said in an interview on the Zach Sang Show. "I look up in the sky and there's a bunch of spaceships.

"I swear to God, there were like five to seven, and I don't know why I didn't like try to take a picture of it"”I just looked at it. I was sitting on a rock, and I was like, 'What in the hell is that?' I was trying to figure it out, and then they went away.. Later, they came back in a different formation," she added. "I was like, 'Those are fucking aliens.' They were spaceships!"

9. Demi Lovato

In an interview with Seth Meyers, the pop star had a couple comments about alien life forms, but then the conversation became even more out of the ordinary.

Demi said she saw an "extremely convincing documentary" on mermaids, and apparently "Christopher Columbus had actually seen three mermaids on his way to America."

Watch the full video of Demi Lovato telling Seth that "it must be really sad for you to not believe that mermaids exist."